Electrical musical instrument



Sept. 24, 1935. A F, KNOBLAUl-l 2,015,363

ELECTRICAL MUSICL INSTRUMENT Filed Feb. 9, 1933 Patented Sept. 24, 1935 ELECTRICAL MUSICAL INSTRUMENT Armand F. Knoblaugh, Cincinnati, Ohio, assignor to The Baldwin Company, Cincinnati, Ohio Application February 9, 1933, Serial No. 655,971

Claims.

My invention relates broadly to the art of transforming the mechanical vibrations of a sonorous body of magnetic material, an example of which would be a vibrating magnetic string, 5 into electrical vibrations, and one object of my invention is to transform the mechanical vibrations of such a body into electrical vibrations by the direct action of said body, when magnetized, upon a conductor or series of conductors in its vicinity. Although a string, bar, or tube 'of hard steel, such asy are employed in many musical instruments, when once magnetized, will retain their magnetism fora considerable length of time,` yet, in view of my first object, it is another object of my invention to provide means whereby the magnetism of the sonorous body may be renewed, as'desired.

The conductor or conductors referred to will preferably be in the form of coils; and a further speciflc object of my invention, therefore, relates to the provision of coils which can serve as devices for producing electrical vibrations in accordance with the movements of the said body and as devices for magnetizing the body; and to the provision ot coil structures which may act in common with a plurality of vibrating sonorous bodies.

The use of the coils as magnetizing devices will preferably involve the passage of direct, or rectified currents through the windings of the coils; and other specific objects of my invention relate to convenient means for applying these currents to the coils. Since my invention may be desirably used in conjunction with an amplifier and since amplifiers, in general, involve devices for supplying direct, or rectified current, a further specific object relates to the economical and eiilcient use of such devices for the furnishing of magnetizing current in my invention, and to switching means for connecting said devices either to the'amplifier or to the above-mentioned coils. The switching means may be manually operated or automatic, and is preferably automatic as shall be shown later in this specification.

Hereinafter in these specifications I shall describe my invention in an exemplary embodiment which employs the strings, keys and strlking mechanism of the piano, it being understood that my invention is not restricted thereto, but is applicable to other instruments having vibrating sonorous bodies of magnetic material.

These and other objects of my invention, which will be set forth hereinafter, or will be apparent to one skilled in the art, upon reading these lto the drawing wherein:

specifications, I accomplish by that certain construction and arrangement of parts and in that method of which I shall now describe the aforesaid exemplary embodiments.v Reference is made The drawing is a sectional view of part of the musical instrument, showing a coil in position over the strings and indicating the connections and devices associated with said coil for causing it to function either as a magnetic charg- 10 ing coil or as a pick-up coil associated with amplification means, the changes in coil function being under automatic control, typified by an automatic switch, shown in action and indicated as a time delay switch.

lIn the exemplary embodiment of my invention which I shall now describe, a musical instrument may be made by using vibrating and tuned magnetic strings I, stretched over a plate 2 of a musical instrument iA and having a coil of cop- 20 per wire 4 associated with the strings I so as to transform intoelectrical vibrations any mechanical vibrations set up in the strings I. The electrical vibrations so generated are amplified by an amplifier 5 and are converted into sound g5 by a loudspeaker 6. l

The instrument shown is an instrument of the piano type, though preferably it will not have the usual sounding board, sov that no diiliculty will be had with acoustic or mechanical feed back. With the elimination of the sounding board it becomes necessary to support the bridge by other suitable means. The bridge may be supported directly upon the plate or some other fixed part of the instrument; or it may be connected to the 35 plate or other support by vibratile or non-vibratile means. In my invention the vibrations of the sonorous body, the strings in this instance, are converted primarily into sound energy by electrical means; and the volume of sound so produced 40 may be controlled by varying the degree of ampliflcation. Thus from a small instrument of the piano type, a volume of sound may be produced equal to or exceeding that of several of the largest piano instruments played simultaneously.

Various arrangements of coils may be used in u the vicinityof the strings I. In the drawing, a single coil 4 is shown, in proximity to the strings and having its magnetic axis substantially normal to the strings. The coil may be used both as a magnetizing means by the passage of suitable direct cr rectified current through the windings of the coil, and as a pick-up means.

The operation of my invention in producing 55 musical tones is as follows: When the keys, not shown, are struck, a piano action, also not shown, is set in motion and causes the strings to vibrate at the frequencies to which they are tuned. 'I'he strings being magnetized, by direct action set up electromotive forces in the pick-up coil, these electromotive forces being applied to the input circuit of amplifier 5. Through the action of amplifier 5, amplified currents are conducted to the loudspeaker 6, to produce musical sounds of pleasing quality, to a radio transmitter for broadcast purposes or to a sound recording device.

It is common practice in the manufacture of pianos to wrap the core wire of the base strings with helices of wire, in order properly to load the strings and yet retain their flexibility. Similarly, in my invention, the bass strings can be wrapped, and I have found it advantageous to use as the wrapping wire, a magnetic material, such as iron or steel.

The vibrating magnetic sonorous bodies which I employ, when magnetized, will retain their magnetism for long periods of time. Yet, since the magnetic effect does decrease with time, it is preferable to provide means to increase or renew it. It is practicable to bias the pick-up coils with direct current, or continuously to apply direct current to a magnetizing coil or coils during the use of the instrument. I prefer, however, to

.diminish the current consumption by using the former may desire, and I provide also automaticv means whereby this current is not applied until after the devices for supplying it have attained sufficient current output.

In the drawing I have shown a switch 26, on the input side of which are conductors 21 and 26, connecting the switch 26 with a commercial source of electric current, which may be alternating current. When the switch 26 is closed, current is fed through conductors 29 and 3|) to a device 3|, which I shall call a power pack. The function of the power pack 3| is to modify the current fed to it by conductors 29 and 39, so as to furnish at the output leads 32 and 33, direct, or rectified current. As the construction of a device such as power pack 3| is well known to the art, I shall not describe it further, noting, however, that while it is indicated as being on a separate chassis from the amplifier 5, it may obviously be mounted wholly or partly upon the same framework as the amplifier. Included in the drawing are conductors 43 and 44, connecting the amplifier 5 with switch 26. Conductors 43 and 44, on the closing of switch 26, furnish current to amplifier 5, for the purpose of heating filaments in vacuum tubes in the amplifier or for other purposes.

I have included in the drawing an automatic switch 45, of the time delay type, the function of which is to perform automatically the operation of magnetically charging the strings and to perform this operation at a predetermined time after the closing of switch 26, Automatic switch 45 may comprise a solenoid 46 connected through conductors 41 and 48 with the power pack 3|, by means of output leads 32 and 33. In the core space of the solenoid 46 is a plunger 49, preferably of laminated steel, and capable of motion Within the solenoid. Attached to plunger 49 is a rod 50,

carrying an insulated member 5| on its central portion and having at its lower end a plunger 52 and a disk 53 adjoining the lower portion of the plunger 52. As shown in the drawing, the lower part of rod 5l) is reduced in diameter, thus forminga shoulder, and is expanded at the end. thus connecting the plunger 52 and the disk 53 to the rodby allowing the said plunger and disk a small freedom of motion, independent of the rod. The plunger 52 operates in a dashpot 54 and has a number of holes 55 through its Ihorizontal portion. Contained in dashpot 54 is a small quantity of oil 56. Imbedded in the insulated member 5| are two metal contacts 51 and 58 that are connected through pigtail connections 59 and 60 and output leads 32 and 33 to the power pack 3|.

Fastened to the bottom of the casing of the switch 45 are two insulated posts 6| and 62 that hold wiping contact members 63 and 64, connected through conductors 65 and 66 and 61 and 68 to the coil 4. Above posts and 62 are two more insulated posts 69 and 10, holding wiping contacts 1| and 12, connected through conductors 13 and 14 to the amplifier 5. Coil-4 is connected to the input circuit of the amplifier 5 through conductors 15 and 16 and conductors 61 and 68.

With the automatic switch in inactive position, the plunger 49 and correlated parts are in the lower position, plunger 52 resting on the bottom of dashpot 54 and all switch contacts being broken. When the switch 26 is closed, current from a commercial source of electric current flows through conductors 21 and 28 and conductors 29 and 3U to the power pack 3|. the power pack, an amount of direct, or rectified, current is conducted through the output leads 32 and 33 and the conductors 41 and 46 to the windings of the solenoid 46, thereby producing a magnetic flux in the core space of the solenoid and magnetizing and attracting upward the laminated steel .plunger 49 contained therein. The motion of the plunger 49 and the correlated parts is impeded, however, by the action of dashpot 54, plunger 52 pressing against disk 53, sealing the holes 55 and allowing a partial vacuum to be created in the dashpot. The leakage of air is reduced by the proximity of the plunger 52 to the inner walls of the dashpot, and by a film of oil from the oil 56. The insulated member 5| thus moves slowly upward and contacts 51 and 58 make electrical connections with wiping contacts 63 and 64 respectively. Direct, or rectified current is then conducted from the power pack 3| through output leads 32 and 33, pigtail connections 59 and 69, contacts 51 and 5B, wiping contacts 53 and 64, conductors 65 and 66 andconductors 61 and 68 to the coil 4, thus allowing coil 4 to magnetize the strings I, a sufficient time having elapsed, due to the action of the delay switch 45 to allow the power pack 3| to develop properly its maximum output. As the insulated member 5| continues its upward motion, the electrical connections are broken between contacts 51 and 56 and wiping contacts 63 and 64, When the member 5| has reached its highest position, the plunger 52 is at the top of the dashpot 54, and contacts 51 and 58 make electrical connections with wiping contacts 1| and 12, thus allowing direct or rectified current to' flow from power pack 3| through leads 32 and 33, pigtail connections 59 and 6U, contacts A51 and 58, wiping contacts 1| and 12 and conductors 13 and 14 to the amplifier 5, thus furnishing direct or rectified By the action of current energy to the amplifier and allowing the 75 graisses coil to function as a pick-up coil iii association with amplifying means.

On opening the switch E6, the plunger @il and correlated parts return quickly to their lower position, plunger and 53 separating slightly, allowing air to pass through tlie holes in my invention ll shall not limit myself to tlie :form of the switch shown. The form exhibited is for purposes of clarity oi explanation. .any auton matic, time delay switcli may loe used.

ln the drawing, the loudspeaker o is shown in conventional form. This loudspeaker may loe plurality oi loudspeakers of any suitable types. li of the moving coil, electrodynamic type, inclinl=a ing magnetic fields maintained by direct, or recti fied current, tlie field coils may lie used in conjunction with any electrical circuits in any weli= known manner. The speaker, or sneakers, may be mounted external to or in the instrument on any suitable baiiie.

lt will be obvious that modifications may loe made in my invention without departing trom tlie spirit thereof.

Having thus described my invention, what 'l claim as new and desire yto secure by letters-Pat ent is:

l. in an electrical musical instrument, a vibratory magnetic sonorous body; a means for magnetizing said body, including in said rneans a coil K of wire; a source oi direct current; and automatic time delay means for connecting said source and said coil. l

il. ln an electrical musical instrument; a vilain.r1 tory magnetic sonorous cody; a ineens for netizing said cody, including in said means a coil oi wire; a source of direct current; and automatic time delay means for causing said source to ener=l glee said coil.7

3. ln an electrical musical instrument, a vibratory rriagnetic sonorous body, a coil ol wire in proximity thereto, an amplifier, a source of direct current, and automatic tirne delay rneans for 4first connecting' said source to said coil and then to said arnpliier.,

fi. ln an electrical musical instrument, a vibratoiy magnetic sonorous body, a coil in. proximity thereto, an amplier, a source of direct current, and automatic time delay means ior iirst connectm ing said source to said coil and tiren to energy a supply terminals o said amplifier.

E. ln an electrical musical instrument, a vibratory magnetic sonorous body; a means for magnetizing said loody, including in said means a coil ot" wire; an amplifier; a source of direct current; and means igor rst connecting said source to said coil and then to said amplifier, the last said means including a time delay automatic switch.

' ARMAND F. KNUBLAUGH.

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